Optimization procedures for a twin controllable pitch propeller of a ROPAX ship at minimum fuel consumption

A propeller optimization procedure is developed by coupling a propeller design tool with a nonlinear optimizer. An optimized propeller contributes toward maritime decarbonization and the mitigation of exhaust emissions from ships. The main objective of this optimization procedure is to select two ducted controllable pitch propellers from the Kaplan 19A series at the service speed for a roll-on/roll-off passenger ship sailing in calm water as a case study. The selected ship is operated by two four-stroke marine diesel engines, each connected to a controllable pitch propeller via a gearbox and a propeller shaft. The propeller selection is performed at the engine operating point with minimum fuel consumption instead of considering only the maximum propeller efficiency. The propeller diameter, pitch, expanded area ratio and rotation speed are optimized as well as the gearbox ratio taking into account the limitations of noise and cavitation criteria. The calculated results from each simulation are compared with the typical procedure used in ship design, which is the selection of the propeller at maximum efficiency. The results show that optimizing the propeller in terms of fuel consumption can reduce the amount of fuel consumed by up to 5.2% rather than only considering the propeller efficiency.